There is a general interest in developing devices often referred to as labs-on-a-chip, which allow users to perform a variety of chemical and biological reactions on a single device. Examples of such devices include flow-based microfluidic devices and droplet-based mixers. Droplet-based mixers can employ, for example, electrowetting based-techniques to facilitate the movement of droplets electrically using electrodes to independently control each droplet. Briefly, electrodes are arranged on a surface (often in a patterned array) and covered by a hydrophobic layer. When an electrode is activated the portion of the hydrophobic layer covering that electrode becomes hydrophilic and attracts a droplet. Each electrode can be thought of as a control pad or location that is hydrophobic until electrode activation when the pad becomes hydrophilic and, thus, water or droplet attracting. Through proper arrangement and control of the electrodes, a droplet can be successively transported between adjacent electrodes. The electrodes can be arranged as an array in any desired pattern so as to allow transport of a droplet to any location covered by that array. Droplet-based devices can be used to perform a variety of droplet operations including, but not limited to, dispensing, mixing and transporting droplets. Droplet-based devices have been developed for performing biological assays including immunoassays and nucleic acid amplification.